ECG Basics Flashcards
What do the points of ecg correlate to P ? QRS? T?
P - Atrial depolaraiation
QRS - ventricular depolarisation
T - ventricular repolarisation
Q R S are
Q first downward deflection
R first upward
S second downward
If QRS has second upwards deflection it is called?
R prime (or RSR)
What is this
QS wave - 1 large negative wave
What waves are here
RS - no negative Q wave
What waves in this complex
RSR (R-prime)
Where are the P QRS and T waves
1 p wave hidden in QRS complex (arrow)
What time interval is a small box? large box?
What about the amplitude?
Assuming paper speed is 25mm/second
1 large box (5mm) - 0.2s
1 small (1mm) - 0.04s
10mm = 1mV
where is the PR interval? What does it measure
Start of P to start of Q
AV conduction time
(time of atrial depolarisation tkes to go through AV node to reach ventricles)
Where is start and end of QT interval
Start of Q to end of T
QT interval here?
Approx 0.44-0.48ms
shows?
p mitrale
Also >0.12s -> LA enlargement
What is this
1st degree AV block
What is the general term for a short PR? 2 Main syndromes?
pre-excitation syndromes
Lown-Ganong-Levine LGL syndrome
- QRS immediately follows p wave
WPW
what is this
Lown-Ganong-Levine LGL syndrome
- QRS immediately follows p wave
WPW with delta wave
R atrial hypertrophy (p wave is > 0.5mV)
ECG dots where does v1-3 represent in the heart
RV
[V2-3 also basal septum]
V2-V4 represent
anterior wall of lV
v5/v6 represent
lateral wall of LV
Where do you place v7-9. What do they represent?
V7 left posterior axillary line,
V8 left mid-scapular line,
V9 at the left paraspinal border
Posterior LV
Whart is the R/S ratio? which leads is it <1 or >1?
<1 usually means corresponds to RV
>1 means usually corresponds to LV
=1 is in transition zone between RV/LV
RS ratio should increase as you go Right to Left
What does the RS ratio here signify
Counterclockwise rotation
RS ratio is shifted right
What is going on with RS ratio here
Clockwise rotation
RS ratio shifted to left
When can you not assess rotation using RS ratios
RBBB
Q wave infarction
WPW
Which ventricle is represented by this?
RV
(Probably v1/v2)
Which ventricle is represented by these leads under normal circumstances?
LV
What is this
M form or RSR pattern
LV leads have this?
M form - note sometimes just notching
LBBB
What does the M form or RSR signify
Delayed conduction - on side of heart where it is seen
2 main causes of RSR (M) patterns
Bundle branch blocks
Dilated / hypertrophic ventricles
Which BBB is this
LBBB - the M form is in v5/6
What is this?
WPW - can be mistaken for RBBB
- Dont fall for the M pattern in V1
What is an incomplete bundle branch block
QRS = 100-120ms
with RSR pattern
LBBB
RBBB
Incomplete RBBB - usually due to Volume overload RV
QRS is .1s with RSR v1
Usual cause of incomplete BBBs
Volume overload of R / L ventricle
RBBB
Which leads are the R waves usually biggest
V5 and v6
How to assess LVH on ECG . Calculate here?
Measure biggest R wave (usually v5/6)
Measure biggest S wave (usually v1/2)
and add them together
- If >3.5mV = positive sokolow index
Here is 2.2mV + 3.1mV = 5.3mV (positive)
How to indicate RVH on ECG
RSS criteria
- R in v1 >0.5mV
- R/S in v1 is >1
- S in v5 is >0.5mV
If 1 correct - possible
If 2 correct - likely
If all 3 correct - very likely
Is there RVH here?
RSS
in V1. R is not >0.5mV
R/S ratio is not >1
S in v5 is not >0.5mV
= No RVH
Is there RVH here?
RSS
in V1. R is 0.6mV
R/S ratio in V1 is >1
S in v5 is >0.5mV (about 1mV)
= likely RVH
LVH - >3.5mV total
[note the negative T waves in v5/6 - indicates LVH with abnormal repolarisation]
LVH >3.5mV total
RVH and LVH
RVH + RV volume overload strain
LVH
LV volume overload (Incomplete LBBB) with strain (inverted T waves)
RVH
LVH + strain
LVH - no strain as positive t waves
What does the ST segment here tell you
Descending ST depression - likely ventricular hypertrophy with repolarisation problem
Usual causes
Sagging ST
1. Digoxin
2. hypokalaemia
3. CAD
usual causes
Horizontal ST depression
-CAD
What is the usual cause of upsloping ST depression
Usually exercise or increased sympathetic tone
Explain t waves here
Note A+B are Asymmetrical - Ventricular hypertrophy
C+D are symmetrical - Ischemia
[All could occur in intraventricular conduction delay]
LBBB
- Note you see the mirror image on the Right sided leads
ie STE in v1 and 2 in LBBB which is due to the ST segment changes in LV
LVH
Note descending asymmetric ST depression in v5/6
RVH with RV strain
LVH
WPW
[Can mimmic LVH or an MI]
Coronary T wave inversion (biphasic T wave)
2 things here
LVH with strain
CAD - biphasic Twaves
What happens to R and Q waves in MI
Q waves develop
R waves get smaller
What happens to QRS in mi? In this example of v1/v2?
Everything pulled down
Q wave gets deeper ie >1/3 of size
R wave gets smaller amplitude
[Pulled down]
What would happen to this complex in v5/v5 if there was infarction
Loss of R wave (as pulled down) and forms a QS complex
What would happen to this complex in v3/v4 if there was infarction?
Newly formed Q wave
What is the normal pattern of Q waves in V4-V6?
What would happen to this ECG if there was a infarct in the septal leads?
Normally the Q gets slightly bigger
In septal infarct it starts big and gets smaller
What would happen here to Q waves with a lateral MI
Qs would be large, but stable in size
Abnormal as there should never be Q waves in any lead with a deep S wave
Which leads usually have an initial small R wave
V1-3
This is a normal QRS in v1-2 what might it look like after MI
Q wave in v1-3 usually pathalogical
[V1-3 should start with an R wave]
What should happen to the amplitude of R wave in V1-6
Should be increasing as there is an increase in the muscular mass of LV
Whats the issue here
There are lateral Q waves
[normal on top]
Whats going on in B
Loss of R wave v2
Q waves v3-v4
Probably scar tissue from old septal infarct
Whats going on in C? What should you check when you see this?
Poor R wave progression v2/3
-> Proably old basal septal infarct (anterioseptal)
[Dont forget to check for RVH with this as may be the cause of a big R wave in v1]
When are q waves abnormal
> 0.04s (1mm)
1/4 of the R wave
RBBB
Anteriolateral infarction
Which of these have a pathological q wave? mi location?
v5-v8 - posteriolateral
Which leads have q waves? What else is seen?
LVH with strain
Anterioseptal MI
Note Q waves in v3-4
QS in v2
Which leads have q waves- MI location? what else is seen?
Anterolateral mi
Q waves v2-5
RBBB
Which leads have q waves - where is MI?
What else is found
V2-3 - anteroseptal
LVH with strain
1st degree AV Block
Where are the pathological q waves - location of mi?
What else is seen
V4-V6 Q waves - anterolateral MI
Complete RBBB
v1-v2 has normal R wave progression
Which leads have q waves? MI location?
q waves - v2 / v3 - anterioseptal
normal r in v1
Where is pathological q waves? mi location?
What else is seen?
Q waves v2-v5 - anteriolateral
RBBB
[Note small R rave normal in v1]
Which precordial leads have q waves? Why?
Septum is first part to depolarise from L->R which is away from leads v4-6
Also seen in I,II,aVF and aVL
Why do MIs produce q waves
When a depolarisation is towards a lead you get a positive deflection
- When away from lead -> negative deflection
Therefore, when myocardium is scarred (post-infarction) it becomes electrically silent and the electrical vector is away from it
[normal v5 vs v5 in lateral scar (in grey)]
Do all MIs produce q waves?
No
Where do the limb leads go?
R - R arm
Lellow - L arm
G L foot
Black R foot
Which direction do leads I,II and III face?
Think X guy
I - L arm
II - L leg
II - R leg
Which direction to the augmented leads read?
Think Y guy
aVL - left arm
aVR - right arm
aVF - foot
aVL = augmented Left
How do leads I-III and augmented leads reflect areas of heart
Think x / y guy for directions
Inferior - III, aVF and II
Lateral - aVL and I
Which leads mirror II, III and aVF?
V1,2,3
Which BBB is here
RBBB
Where is the MI
Anterolateral and inferior wall
Where is the MI?
Inferior
Q wave in II
QS in III and aVF
Note mirror image of leads v1-v3 (taller R and big positive T waves)
[borderline for LVH too]
What do you see
1st degree AV block
Inferior/lateral/posteiror MI
QS in v2,v3
Q wave v4,v5
STE inferior
Whats the main difference in ST segment changes vs q waves with regards to an MI
Q waves represent scar tissue so are usually permanent
STEMI vs NSTEMI vs unstable angina
Which has a troponin release?
NSTEMI / STEMI have trop release
note unstbale angina may have ECG changes
What is the usual path of ST segment changes in MI following STEMI if they recover
STEMI -> TWI -> ST isoelectric -> T wave normalisation
L side with Q waves, right without
Trop rise
NSTEMI in the territory of the left anterior descending artery (LAD). Leads V2, V3, and V4 are affecte
Chest pain of short duration (15 to 20 minutes) and
appears at rest or even during sleep with these ECG changes
Variant angina or Prinzmetal angina
How to differentiate STE in pericarditis vs STEMI
Pericarditis usually concave + ST segment originates from ascending part of the QRS
STEMI convex / flat
ST segment from descending part of QRS
When might you get a STE which lasts forever
Myocardial aneurysm EG post mi
Pericarditis - note STE in v2-v6
V2-4 - LAD
V5-6 - Cx
[Unlikely both are occluded at the same time]
Also Concave and STE comes from ascending part of QRS which is typical of pericarditis
These changes occur only when HR in 60s and resolve on increasing rate. No chest pain.
Vagotonia / High take off
-due to Early repolarisation
Usually has high T waves
How do you use j point to differentiate hyperkalemia and vagotonia as both have peaked t waves
J point elevated in vagotonia
What is going on here
Pericarditis
Note initial STE in v2-5 coming from ascending QRS and concave shape
In resolution STE coming down and has negative T waves
chest pain
anteriolateral NSTEMI
Acute anteriolateral STEMI
note loss of r waves in v2 and 3
inferiolateral STEMI
q wave STEMI
Note loss of r wave in v2-5 with QS complexes
inferior STEMI
note Q waves in anterolateral (probably old infarct - chronic)
1st degree av block
LVH with strain
note the R which looks smaller in V3 is actually proportionally getting bigger = normal
Which block? Ischaemia?
LBBB
- LBBB usualy has negative T waves but here there is raised
-> probably acute ischemia interiolateral STEMI
With Axis which lead is at 0 degrees? Where are the rest
Lead I
What is a normal cardiac axis? how can you tell this easily?
between –30° and +90° is called a “normal axis”
if I and II are both positive
If I is positive and II is negative - what is the axis?
The area between –30° and –90° is called “left axis deviation”
If I is negative and aVF is positive?
The area between +90° and +/–180° is called “right axis deviation”
both leads I and aVF are negative?
The area between –90° and +/–180° is called a “northwest axis”
If lead I is positive which lead do you use to work out if there is an axis deviation?
If it is negative?
Which leads are pos / neg for:
normal axis?
LAD?
RAD?
NWA?
Normal - I and II positive
LAD - I is positive and II is negative
RAD - I is negative and aVF is positive
NWA - leads I and aVF are negative
What is the breakdown of the bundles for ventricular depolarisation?
Bundle of his
-> Right bundle
->Left bundle -> Left posterior fascicle + left anterior fascicle
What is a bifasicular block? how does it appear on ECG?
RBBB + block of one of the L fascicles
RBBB + LAD = RBBB + LAFB
RBBB + RAD = RBBB + LPFB
How can you use axis deviation to help with suspicion of RVH?
If RSS criteria are positive (e.g., you have a patient with a tall R in V1 and a deep S in V5) + RAD
-> More likely there is RVH
LVH on ecg with RAD probably means?
Biventricular hypertrophy
What is p mitrale - where is it most pronounced?
LA hypertrophy
P wave has two peaks, and usually, the second peak is taller than the first one.
P-wave duration is greater than 0.1 seconds.
These changes are most pronounced in leads I and II.
Bar leads I and II where else is good to look for LAH?
V1 - look for a biphasic p wave
If the negative part is longer than 1 small box (or >0.04 s), then P mitrale is present
How do you assess RAH on ECG? which leads are best? What is is called?
Right atrial hypertrophy has peaked p waves in leads II, III, and aVF >0.25mV
- p-pulmonale
What do the p waves in v1 and II look like normally? in RAH? LAH?
What is a low voltage ECG? usual causes
none of the QRS complexes in the standard leads (i.e., leads I, II, and III) is higher than 0.5 mV
- peripheral edema, cardiac amyloid, pulmonary emphysema, large pericardial effusion, or severe myocardial damage
Which leads are positive or negative for all of the axis deviations
Which leads are best to look for atrial depolarization
v1 - as will be positive in RA depolarization followed by negative in LA Depolarisation
II - as points in the same direction -> biggest p wave to assess
What is the axis here
borderline LAD
Axis here?
Probably limb lead reversal with normal axis
note negative p in lead I / aVR and positive p in III
What block
I positive and II negative -> LAD
PR prolonged -> 1st degree AV block
QRS prolonged with RSR v1 -> RBBB
LAD + RBBB = bifasicular block + 1st AV block
This is termed incomplete trifasicular block
What is trifasicular block? implications
Right bundle branch block
Left axis deviation (Left anterior fascicular block)
Third degree heart block
-> PPM
Trifasicular block
Right bundle branch block
Left axis deviation (Left anterior fascicular block)
Third degree heart block
syncope
Trifasicular block
Right bundle branch block
Left axis deviation (Left anterior fascicular block)
Third degree heart block
-> PPM
Incomplete trifasicular block
[Bifascicular block + first degree AV block]
Right bundle branch block
Left axis deviation (= left anterior fascicular block)
First degree AV block
Axis? what else is seen?
p mitrale I, II -> LAH
LVH
RVH with strain
Axis? what else is seen?
I neg, II pos -> RAD
II, III -> p pulmonale -> RAH
R in v1 >0.5mV, s in v5 >0.5mV -> RVH
HyperK ECG
Tall T waves
-> widening of QRS if severe
Hypokalaemia ECG
T flattening
Sometimes ST depression
U wave ( second wave following T)
T waves in hyper vs hypo kalaemia
Classic mistake made when measuring QT interval in hypoK?
people measure QU interval rather than QT
Key hypoCa finding? HyperCa?
HypoCa - Prolonged QT
HyperCa - shortened QT
A simple way to say if QT is prolonged
Measure half way between RR inverval -> if end of QT in first half its normal
if in 2nd half abnormal
Is this QT prolonged?
no
is this QT prolonged?
YES
Which electrolyte is classic for short QT
HyperCa
How to calculate rate on ECG ? In this eg?
300 / large squares between RR interval
approx 300/5 = 60
[slightly more so approx 62-64]
Whats the rate here?
300/2.2
approx 136
How many big boxes between RR intervals for rate of 75?
4
Axis? electrolye? rotation? anything else?
RAD
HyperK
Clockwise rotation - transition zone in v5
RAH -
Axis? What is enlarged? rotation?
RAD
RAH
RVH - with strain [ the t-wave inversion going all the way to v5 is due to the extension of the RV there]
Clockwise - transition in v5
Axis? Enlargement? Block?
RAD
P mitrale -> LAH
RBBB -> bifasicular block (posterior fascicle)
Axis? electrolyte? elargement rotation?
normal axis
HypoK - STD with combination of T and U
LAH - p mitrale in I, II
Clockwise rotation
Axis? Enlargement? block?
RAD
RVH
RBBB
=bifasicular block (L posterior fasicle)
Axis? block? anything else?
RAD
RBBB
Deep S I, deep Q III, TWI III
S1QIIITIII
-> PE
Axis? Block? anything else?
LAD + RBBB -> bifasicular block (L anterior fasicle)
STEMI
Axis? What else?
LAD
PR short with delta in eg v2 = WPW
What are the criteria for sinus rhythm
P waves are positive in leads I and II
Every p is followed by a QRS
The time between p waves and QRS is constant
The distances between QRS are constant
Axis? block?
LAD
RBBB
1st degree AV block
= incomplete trifasicular block
Axis
Borderline rightward
RAH
RVH
